Due to increases in capacity and degree of integration of semiconductor devices, semiconductor devices are gradually decreasing in area. Accordingly, to reduce metal wirings in semiconductor devices and a width of the metal wirings in accordance with a reduced area of semiconductor devices, there exists a need for stacked multi-layered metal wirings, i.e., metal wirings that are stacked one above another in multiple layers. Formation of such multi-layered metal wirings essentially necessitates flattening an interlayer insulating film formed on and/or over a lower metal wiring. However, due to the fact that some regions are densely formed with metal wirings, whereas some regions have no metal wirings, flattening, in other words, leveling the uppermost surface, of the interlayer insulating film formed on and/or over the lower metal wiring is difficult. To solve this problem, dummy patterns may be formed in regions having no metal wirings. However, dummy patterns may cause undesirable parasitic capacitance with metal wirings adjacent thereto.